The objective of these experiments is to elucidate the effects of fetal cocaine exposure on neuronal development. Infants which are born to mothers who use cocaine, have increased risk of neurological and neurobehavioral deficiencies. These deficits imply that dopamine neurotransmission is altered. In adult animals cocaine inhibits reuptake of monoamines and thus, affects dopamine neurotransmission. However, very little is known about the effects of cocaine on developing neurons. In order to characterize cocaine-induced changes in brain development, we will focus on the dopaminergic neuronal systems, and explore the effects of cocaine on the molecular, cellular and structural changes that occur during the early stages of neuronal proliferation and migration. The first series of experiments will examine the effects of cocaine on the early ontogeny of tyrosine-hydroxylase (TH)-containing neurons destined to form the mesolimbic, nigrostriatal and tuberoinfundibular dopaminergic neuronal groups. We will determine the time of origin, anatomical location and maturation of cells containing TH within the ventral tegmental/substantia nigra and hypothalamic areas, and the development of their fiber projections using immunocytochemistry and in situ hybridization. Secondly, we will explore the effects of cocaine on the ontogeny of dopamine receptors in the nigrostriatal/mesolimbic and hypothalamic systems. We will detect and quantify D-1 and D-2 receptor mRNAs and measure receptor binding in the nucleus accumbens/striatum and the hypothalamus during the early phase of dopaminergic neuronal development. These experiments will be performed using in situ hybridization and polymerase chain reaction (PCR) to localize and quantify and mRNAs, and receptor autoradiography to quantify receptor binding. The effects of cocaine on the development of the dopamine transporter will also be investigated using [3H]CFT (WIN 35,428) as a ligand. The next series of experiments will examine the effects of cocaine on the ontogeny of dopaminergic target neurons, focusing on enkephalin neurons in the nucleus accumbens and the striatum, and on GnRH neurons in the hypothalamus. These experiments will be performed using immunocytochemistry and in situ hybridization to study the maturation of peptide expression and migration. Lastly, we will quantify proenkephalin mRNA and GnRH mRNA during peak migration and during the post migration period in control and cocaine- treated fetuses, using PCR. The results from these studies will provide important information about normal development and the effects of cocaine on major dopaminergic neuronal systems and their target neurons. Therefore, information will be generated to understand the basic effects of cocaine on developing neurons. This data can be used to develop treatment strategies to counter the effects of cocaine in infants and young children.